Commit-ID: 5bce9db1894c998c5b85a34036d679ea6517668f Gitweb: https://git.kernel.org/tip/5bce9db1894c998c5b85a34036d679ea6517668f Author: Alexander Shishkin <alexander.shish...@linux.intel.com> AuthorDate: Tue, 29 Aug 2017 17:01:03 +0300 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Fri, 29 Sep 2017 13:28:30 +0200
perf/core: Explain perf_sched_mutex To clarify why atomic_inc_return(&perf_sched_events) is not sufficient and a mutex is needed to order static branch enabling vs the atomic counter increment, this adds a comment with a short explanation. Signed-off-by: Alexander Shishkin <alexander.shish...@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Link: http://lkml.kernel.org/r/20170829140103.6563-1-alexander.shish...@linux.intel.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- kernel/events/core.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/events/core.c b/kernel/events/core.c index 6bc21e2..5ee6271 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -9394,6 +9394,11 @@ static void account_event(struct perf_event *event) inc = true; if (inc) { + /* + * We need the mutex here because static_branch_enable() + * must complete *before* the perf_sched_count increment + * becomes visible. + */ if (atomic_inc_not_zero(&perf_sched_count)) goto enabled;
